Methods: This retrospective study was done to identify discordances between CTX microdilution (MD) MICS and Etest MICs, and to evaluate CTX treatment outcomes of patients with MSSA bacteremia in an inner city hospital. Microbiology records were reviewed for a 14-month period to identify patients with MSSA bacteremia that had both MD and Etest MICs reported. Patient demographics, comorbid conditions, site of infection, length of stay, presence of indwelling devices, source of bacteremia, antibiotic therapy, microbiological and clinical outcomes were collected from the electronic medical record. Data was analyzed using descriptive and univariate analysis.
Results: A total of 21 patients were identified with MSSA bacteremia and both CTX MD and Etest MIC results. MD MICs were <8 µg/ml (susceptible) for all MSSA strains; 9 (42%) of these strains were resistant by Etest (MIC >8 µg/ml). Mean age was 54 years and the most frequent comorbid conditions were HIV infection (24%), diabetes (24%), and chronic kidney disease (24%). Skin or soft tissue abscesses were the most common source of bacteremia identified (33%). 6 of 21 patients were treated with CTX; 3 had MSSA strains that were resistant by Etest (MIC >8 µg/ml). There were 3 CTX treatment failures; only one of the strains was CTX resistant by Etest.
Conclusion: CTX is not uncommonly used to treat MSSA bacteremia in our institution. CTX MICs by Etest are frequently discordant (and higher) when compared to standard MD methods. CLSI does not recommend routine CTX susceptibility testing for MSSA and the impact on treatment outcomes has not been established. Additional studies on the optimal method for determining CTX susceptibility and the role of CTX for MSSA bacteremia are needed.
L. Dever, None
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